NameNode Federation
What is NameNode Federation ? The NameNode keeps track of each and every file that is present on its file system. All this information is stored in main memory. As the no of files keep increasing within the cluster, the main memory would get filled up at some point of time. In order to address this issue, what Hadoop does is.. It uses multiple NameNode to manage each portion of the file system. Example: Let us say, we have three NameNode as part of NameNode federation. - First NameNode could be dedicated to Sales data. - Second NameNode could be dedicated to Account data. - And third NameNode could be dedicated to HR data. So, Unique Id will get created for each NameNode called block pool id. If any NameNode goes down, it does not affect other NameNode.